Method for testing switch in advance pneumatic detector

ABSTRACT

A method for testing a switch in an advance pneumatic detector with a pressure tube includes moving a piston within the pressure tube with a magnet. A pressure of a gas in a portion of the pressure tube is adjusted in response to moving the piston. A state of the switch is monitored.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. application Ser. No. 15/383,390filed Dec. 19, 2016 for “IN-SITU FUNCTIONALITY TEST FEATURE FOR ADVANCEPNEUMATIC DETECTOR” by D. L. Seebaluck and A. S. Rogers.

BACKGROUND

The present disclosure relates to an advance pneumatic detector (“APD”).In particular, the disclosure relates to an APD with a test feature fordetecting the state of the APD.

An APD is typically comprised of both an alarm switch and a faultswitch. APDs can utilize a pressure tube that contains a gas that willexpand as it is heated, thus increasing the pressure in the pressuretube. An alarm switch is used to indicate overheat or fire situations.An alarm switch includes a deformable diaphragm that is at a normalstate when the system is at a normal pressure. As the pressure increasesin the pressure tube, the diaphragm deforms and closes an electricalcircuit, indicating that there is an alarm condition in the system. Afault switch is used to indicate whether there are leaks, disconnects,or other problems in the APD. A fault switch includes a deformablediaphragm that is deformed when the system is at a normal pressure. Ifthe pressure drops below normal, the diaphragm of the fault switchresumes its normal state and opens an electrical circuit, indicatingthat there is a fault condition in the system.

APDs utilizing both an alarm switch and a fault switch are used onaircraft to detect alarm and fault conditions. The pressure tubes forthe alarm and fault switches can typically run anywhere from one footlong to fifty feet long, and can be placed in systems that are prone tooverheating or fires. With existing APDs used in aircraft applications,such as in the engine or wing, there are no current designs that allowfor in-situ testing to verify and confirm whether a switch of the APD isstill functioning. Currently, to determine whether the APD isfunctional, the APD must be removed from the aircraft and subjected tohigh heat or extreme cold (e.g., liquid nitrogen bath) in order to resetthe switch and/or provide indication for a low-pressure state or latentfailure mode.

SUMMARY

An advance pneumatic detector to indicate pressure changes in anenvironment includes a switch, a pressure tube, an endcap, a piston, anda magnet. The pressure tube is connected to the switch. The endcap isdisposed on an end of the pressure tube opposite from the switch. Thepiston is disposed within and forms a seal against the pressure tube.The piston is slidably engaged with the pressure tube. The magnet isslidably attached to and surrounds a portion of the pressure tube. Themagnet is configured to control the positioning of the piston within thepressure tube.

A method for testing a switch in an advance pneumatic detector with apressure tube includes moving a piston within the pressure tube with amagnet. A pressure of a gas in a portion of the pressure tube isadjusted in response to moving the piston. A state of the switch ismonitored.

A method of assembling an advance pneumatic detector includes placing apiston within a pressure tube of a switch of the advance pneumaticdetector. The switch is charged with gas. The switch is hermeticallysealed. The advance pneumatic detector is calibrated. A magnet ispositioned to surround a portion of the pressure tube such that themagnet is slidably engaged with the pressure tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of an APD with a switch, apressure tube, and a piston.

FIG. 1A is a side cross-sectional view of the APD of FIG. 1 with theswitch in a first position.

FIG. 1B is a side cross-sectional view of the APD of FIG. 1 with theswitch in a second position.

FIG. 1C is a side cross-sectional view of the APD of FIG. 1 with theswitch in a third position.

FIG. 2A is a side cross-sectional view of the APD of FIG. 1 with thepiston in a first position.

FIG. 2B is a side cross-sectional view of the APD of FIG. 1 with thepiston in a second position.

FIG. 2C is a side cross-sectional view of the APD of FIG. 1 with thepiston in a third position.

FIG. 3 is a flowchart illustrating a method of assembling the APD ofFIG. 1.

DETAILED DESCRIPTION

In general, the proposed APD incorporates a pressure tube with amagnetic piston element, the position of which is controlled by a magnetexternal to the pressure tube. Without needing to remove the APD fromthe aircraft, the magnet can be moved longitudinally along to thepressure tube in order to move the piston and change the pressure in thepressure tube thereby tripping the switch. The benefit of the proposedAPD is the elimination of the requirement of removing the APD from theaircraft thereby saving large amounts of time during routine inspectionsof the aircraft.

FIG. 1 shows a side cross-sectional view of APD 10. APD 10 includesswitch 12, housing 14 (including first retainer portion 16 and secondretainer portion 18), contact pin 20, fault diaphragm 22, alarmdiaphragm 24, insulator 26, insulator 28, cavity 30, pressure tube 32(including first chamber 34, second chamber 36, internal stops 38, andexternal stops 40), endcap 42, piston 44 (including passage 46), magnet48, power source 50, and electronic controller 52. APD 10 also includespath A, path B, path C, and path D. Similar configurations are disclosedin U.S. patent application Ser. Nos. 13/836,675, 14/287,969, and14/515,886 by Applicant Kidde Technologies, Inc., which are incorporatedherein by reference in their entirety.

APD 10 is a linear thermal sensor with integrated alarm and faultswitches. Switch 12 is a discrete pressure switch configured to detectchanges in pressure within switch 12 due to temperature changes externalto switch 12. Housing 14 is a rigid casing that encloses switch 12.First retainer portion 16 and second retainer portion 18 are portions ofhousing 14. First retainer portion 16 and second retainer portion 18 areconstructed out of a refractory metallic material that is capable ofconducting an electrical signal. Refractory materials are used so thatfirst retainer portion 16 and second retainer portion 18 can maintaintheir strength when first retainer portion 16 and second retainerportion 18 are subject to high temperatures. Contact pin 20 is a rod ofsolid, electrically conductive material. In one non-limiting embodiment,contact pin 20 is formed of metallic material.

Fault diaphragm 22 and alarm diaphragm 24 are semi-rigid deformablesheets of solid electrically conductive material. Fault diaphragm 22 andalarm diaphragm 24 can be constructed out of refractory metallicmaterials. Fault diaphragm 22 and alarm diaphragm 24 can have anythickness that allows fault diaphragm 22 and alarm diaphragm 24 todeform. Fault diaphragm 22 has a smaller thickness in the embodimentshown so that it deforms at lower pressures than alarm diaphragm 24.This allows switch 12 to be used to indicate different pressure levelscorresponding to alarm and fault conditions. Insulator 26 and insulator28 are pieces of solid material. Insulator 26 and insulator 28 can bemade of any material that is capable of acting as an electricalinsulator. Cavity 30 is a space within housing 14 that is incommunication with pressure tube 32.

Pressure tube 32 is a tube of solid material containing an inert gassuch as helium or hydrogen. In one non-limiting embodiment, pressuretube 32 includes a metallic material such as stainless steel 321.Pressure tube 32 can have a typical length between 0.305 meters (1 foot)and 15.24 meters (50 feet) depending on where APD 10 will be used. Adiameter of pressure tube 32 can include approximately 0.063 inches(1.600 millimeters). First chamber 34 and second chamber 36 are hollowportions of pressure tube 32 on opposite sides of piston 44. Internalstops 38 are pieces of solid material extending radially inward formpressure tube 32. External stops 40 are pieces of solid materialextending radially outward from pressure tube 32. Endcap 42 is a coverincluding a solid material that seals the outer end of pressure tube 32.

Piston 44 is a disk or cylinder of solid material. In one non-limitingembodiment, piston 44 includes a material that is metallic and/ormagnetized such as a permanent magnet or an electromagnet. Passage 46 ischannel configured to communicate a fluid (the gas within pressure tube32) between first chamber 34 and second chamber 36. Magnet 48 is a pieceof solid material that is magnetized and is longitudinally movable alongthe exterior of pressure tube 32. Magnet 48 can include a permanentmagnet or an electromagnet. In one non-limiting embodiment, magnet 48includes a series or combination of permanent magnets and/orelectromagnets disposed along pressure tube 32. Magnet 48 can include acuff or cylindrical shape. Power source 50 is any power source capableof supplying electric power to switch 12. Electronic controller 52 is acontroller for sending and receiving electrical signals. Electroniccontroller 52 is configured to alert the pilot of a thermal or firecondition.

In one non-limiting embodiment, APD 10 is installed on an aircraft inone of the main landing gear wheel wells, the main engine, or theauxiliary power unit. Switch 12 includes housing 14 that is constructedof first retainer portion 16 and second retainer portion 18. Firstretainer portion 16 and second retainer portion 18 are connected to oneanother with insulator 26 positioned between them so that retainerportions 16 and 18 are electrically isolated from one another. Housing14 includes cavity 30 that is bound by first retainer portion 16, secondretainer portion 18, and insulator 26. First retainer portion 16contains contact pin 20 with insulator 28 running between first retainerportion 16 and contact pin 20. Second retainer portion 18 containspressure tube 32.

Contact pin 20 is held in first retainer portion 16 with insulator 28running between contact pin 20 and first retainer portion 16. Faultdiaphragm 22 and alarm diaphragm 24 are held between first retainerportion 16 and second retainer portion 18 in cavity 30. Fault diaphragm22 is held in switch 12 between insulator 26 and second retainer portion18. Alarm diaphragm 24 is held in switch 12 between first retainerportion 16 and insulator 26. Insulator 26 is located between firstretainer portion 16 and second retainer portion 18 to insulate the twoportions and to prevent electrical signals from being passed betweenthem. Insulator 28 is located between first retainer portion 16 andcontact pin 20 to insulate them and to prevent electrical signals frombeing passed between them. Cavity 30 is positioned between firstretainer portion 16 and second retainer portion 18.

Pressure tube 32 runs through second retainer portion 18 and fluidlyconnects to cavity 30. Pressure tube 32 also extends into cavity 30.Pressure tube 32 is capped on an end opposite from switch 12 by endcap42. First chamber 34 and second chamber 36 are located within pressuretube 32 and are separated by piston 44. First chamber 34 and secondchamber 36 are fluidly connected via passage 46. First chamber 34 isfluidly connected to cavity 30 of switch 12. First chamber 34 isdisposed between housing 14 and piston 44. Second chamber 36 is disposedbetween piston 44 and endcap 42. Internal stops 38 are connected to aninner surface of pressure tube 32 and extend into a pathway of piston44. External stops 40 are connected to an external surface of pressuretube 32 and extend into a pathway of magnet 48. In a non-limitingembodiment, external stops 40 can be integrally formed with pressuretube 32. In another non-limiting embodiment, external stops 40 can beremovably attached onto pressure tube 32. Endcap 42 forms a mechanicaland hermetic seal with an end of pressure tube 32 opposite from switch12.

Piston 44 is disposed within and forms a seal against pressure tube 32.Piston 44 is slidably engaged with pressure tube 32. Piston 44 dividespressure tube 32 into first chamber 34 and second chamber 36. Passage 46extends through piston 44 and fluidly connects first chamber 34 andsecond chamber 36 of pressure tube 32. Magnet 48 extends around at leasta portion of pressure tube 32. Magnet 48 is slidably attached to andsurrounds a portion of pressure tube 32. Magnet 48 is configured tocontrol the positioning of piston 44 due to a magnetic field of magnet48 interacting with piston 44 and applying a magnetic force, whichcauses piston 44 to move within pressure tube 32. In one non-limitingembodiment, magnet 48 is attached to pressure tube 32 after APD 10 isinstalled onto the aircraft. In another non-limiting embodiment, magnet48 is attached to pressure tube 32 before APD 10 is installed onto theaircraft.

Power source 50 is connected to fault diaphragm 22 along path A.Electronic controller 52 is connected to alarm diaphragm 24 along path Band to contact pin 20 along path C. Path D exits electronic controller52 to send a signal to an electronic component that will indicate whattype of pressure conditions are present in switch 12. These electroniccomponents can include electrical equipment in the cockpit of anaircraft.

Pressure tube 32 contains a gas that expands as it is heated, thereforeas pressure tube 32 is heated the pressure in pressure tube 32 willincrease. As the pressure in pressure tube 32 increases, the pressure incavity 30 will also increase. The pressure in cavity 30 can cause faultdiaphragm 22 and alarm diaphragm 24 to deform. In the embodiment shownin FIG. 1, there is no pressure in switch 12 and fault diaphragm 22 andalarm diaphragm 24 are in their normal configuration (for example,occupying a convex shape towards pressure tube 32). Pressure tube 32will be placed next to aircraft components that are capable ofoverheating or components where a fire could occur, such as the landinggear wheel well, the engine, or the auxiliary power unit.

The state of switch 12 is tested by activating switch 12 due to a changein pressure in pressure tube 32 caused by movement of piston 44 bymagnet 48. As magnet 48 is moved in longitudinal direction (right toleft in FIG. 1) relative to pressure tube 32, the magnetic field ofmagnet 48 interacts with piston 44. Movement of magnet 48 causes piston44 to move linearly within pressure tube 32. As piston 44 is moved,pressure of a gas within first chamber 34 of pressure tube 32 isadjusted in response moving piston 44. The gas in first chamber 34becomes compressed which in turn increases the pressure of the gaswithin first chamber 34 and cavity 30. At least one of fault diaphragm22 and alarm diaphragm 24 can be activated in response to the pressureadjustment of the gas in pressure tube 32 and cavity 30. An electricalsignal is activated to indicate the state of fault diaphragm 22 andalarm diaphragm 24.

Internal stops 38 protrude into the pathway of piston 44 and preventpiston 44 from moving too close to housing 14. Internal stops 38mechanically prevent piston 44 from moving past a certain point inpressure tube 32. Likewise, external stops 40 protrude into the pathwayof magnet 48 and prevent magnet 48 from moving too close to housing 14.External stops 40 mechanically prevent magnet 48 from moving past acertain point along pressure tube 32.

For example, as magnet 48 is moved towards housing 14, piston 44 alsomoves towards housing 14 in response to the moving magnetic field of andcorresponding change in magnet force from magnet 48. As piston 44 movestowards housing 14, the pressure within first chamber 34 and cavity 30increases which deforms at least one of fault diaphragm 22 and alarmdiaphragm 24. Conversely, as magnet 48 is moved away from housing 14,piston 44 also moves away from housing 14 in response to the movingmagnetic field of and corresponding change in magnet force from magnet48. As piston 44 moves away from housing 14, the pressure within firstchamber 34 and cavity 30 decreases which causes at least one of faultdiaphragm 22 and alarm diaphragm 24 to form back into its originalun-deformed convex shape.

Passage 46 provides a restricted orifice, weep hole, or bleed passage,which allows the gas pressure within pressure tube 32 to equalize acrosspiston 44, for example as between first chamber 34 and second chamber36. Passage 46 acts as a pressure relief mechanism by permitting piston44 to move and overcome the counter-acting pressure of cavity 30.Passage 46 permits a time delay for testing to satisfy an alarm or faultpersistence filter of electronic controller 52. During operation of theaircraft, passage 46 allows a small amount of time during the changestate of piston 44 so that the controller in the cockpit can observe thefault/alarm state of APD 10.

In one non-limiting embodiment, a first mechanic monitors an engine firepanel in the cockpit while a second mechanic activates piston 44 withmagnet 48 and moves piston 44 to one of internal stops 38. Depending onthe direction of activation (movement) of piston 44, the pressure incavity 30 increases or decreases as a step function, then decays as theseepage via passage 46 equalizes the pressure in pressure tube 32 onboth sides of piston 44. Thus, the first mechanic in the cockpitobserves the engine fire panel alarm light go from OFF to ON to OFF,which indicates that switch 12 was activated into both states. The firstmechanic then tells the second mechanic to move piston 44 with magnet 48to another stop and the process is repeated for to indicate an integrityor fault condition.

With existing APDs, once they are bolted onto the aircraft they maynever change state and can be attached to the aircraft for 25+ yearswith no means for checking the state of the switch. Existing APDsrequire complete removal of the APD from the aircraft in order to assessthe states of the diaphragms in the switch. Existing APDs must beremoved completely from the aircraft and inserted into a hightemperature oven or kiln to exercise the alarm switch and thenintroduced into dry ice or liquid nitrogen to lower the gas pressuresufficiently to exercise the fault switch. This process is undesirablefor the aircraft service and maintenance due to the large amount of timeit takes to remove the APD assembly from the aircraft.

With piston 44 and magnet 48, a state of APD 10 can be tested withoutthe need for removing APD 10 entirely from the aircraft. Piston 44 andmagnet 48 provide a non-invasive means of going out onto the aircraft,opening up an area of the aircraft containing APD 10, and charging thegas pressure in first chamber 34 of pressure tube 32 with piston 44, andmodulate the pressure in pressure tube 32 to activate switch 12 intodifferent test, alarm, fault, or normal states. Additionally,pre-installing magnet 48 onto pressure tube 32 helps to limit the amountof ground support equipment necessary during servicing of the aircraft.

FIG. 1A is a side cross-sectional view of switch 12 in system 40 atnormal pressure conditions during operation of the aircraft. In theembodiment shown, normal pressure conditions exist under normaloperating temperatures. Normal operating temperatures exist between apre-set fault temperature and a pre-set alarm temperature. The pre-setfault temperature defines a lower limit of the normal operatingtemperatures and is the point at which pressure conditions will dropbelow normal. Fault diaphragm 22 will deform when the temperature risesabove the pre-set fault temperature. The pre-set alarm temperaturedefines an upper limit of the normal operating temperatures and is thepoint at which pressure conditions will rise above normal. Alarmdiaphragm 24 will deform when the temperature rises above the pre-setalarm temperature. Normal pressure conditions thus exist between thepre-set fault temperature and the pre-set alarm temperature. At normalpressure conditions, fault diaphragm 22 deforms and comes into contactwith alarm diaphragm 24.

Under normal pressure conditions, an electronic signal is being sentthrough fault diaphragm 22 from power source 50. When fault diaphragm 22comes into contact with alarm diaphragm 24 under normal pressureconditions, an electrical circuit between the two is closed and theelectrical signal from power source 50 will travel through faultdiaphragm 22 to alarm diaphragm 24. This electrical signal can thentravel through alarm diaphragm 24 and along path B to electroniccontroller 52. Electronic controller 52 will register this electricalsignal and will send out a signal along path D indicating that there arenormal pressure conditions in switch 12.

Utilizing switch 12 in pneumatic detectors is advantageous, as switch 12can send a signal that indicates a system is at a steady state. Thisallows a user to verify that the pneumatic detector is operable and thatthe system is functioning normally.

FIG. 1B is a side cross-sectional view of the integrated switch of FIG.1A at a higher than normal pressure conditions during operation of theaircraft. Above normal pressure conditions exist at temperatures abovethe pre-set alarm temperature. In the embodiment shown, the pre-setalarm temperature of the sensor is 316 degrees Celsius (600.00 degreesFahrenheit). Temperatures above the pre-set alarm temperature of thesensor will cause above normal pressure conditions. In alternatenon-limiting embodiments, the pre-set alarm temperature of the sensorcan vary based on the thickness of alarm diaphragm 24 in switch 12 andthe quantity of gas contained in pressure tube 32. At above normalpressure conditions, both fault diaphragm 22 and alarm diaphragm 24 willdeform. This will cause fault diaphragm 22 to come into contact withalarm diaphragm 24 and it will cause alarm diaphragm 24 to come intocontact with contact pin 20.

In operation, an electronic signal is being sent through fault diaphragm22 from power source 50. When fault diaphragm 22 comes into contact withalarm diaphragm 24 under normal pressure conditions, an electricalcircuit between the two is closed and the electrical signal from powersource 50 will travel through fault diaphragm 22 to alarm diaphragm 24.When alarm diaphragm 24 comes into contact with contact pin 20, anelectrical circuit between them is closed and the electrical signal willtravel through alarm diaphragm 24 to contact pin 20. This electricalsignal can then travel through contact pin 20 and along path C toelectronic controller 52. Electronic controller 52 will register thiselectrical signal and will send out a signal along path D indicatingthat there are above normal pressure conditions in switch 12.

Above normal pressure conditions can occur when there is a fire oroverheat condition in a component, such as an engine, landing gear wheelwell, or auxiliary power unit. Pressure tube 32 can run along thesecomponents. As the heat rises in or around the components, the pressurein pressure tube 32 will increase, which will increase the pressure incavity 30 of switch 12. If the temperatures get above the pre-set alarmtemperature, the pressure will get high enough to cause alarm diaphragm24 to deform and come into contact with contact pin 20. This closes thecircuit between alarm diaphragm 24 and contact pin 20 and causes anelectrical signal to travel between the two. This signal will be sent toelectronic controller 52. Electronic controller 52 can then send asignal indicating that there is an alarm condition in switch 12.

FIG. 1C is a side cross-sectional view of the integrated switch of FIG.1A at a lower than normal pressure condition during operation of theaircraft. Below normal pressure conditions exist at temperatures belowthe pre-set fault temperature of the sensor. In the embodiment shown,the pre-set fault temperature of the sensor is −54 degrees Celsius (−65degrees Fahrenheit), which is the temperature at a lower limit of thenormal operating temperatures. Temperatures below the pre-set faulttemperature of the sensor will cause below normal pressure conditions.In alternate embodiments, the pre-set fault temperature of the sensorcan vary based on the thickness of fault diaphragm 22 in switch 12. Atbelow normal pressure conditions, both fault diaphragm 22 and alarmdiaphragm 24 will be in their normal configuration and they will not betouching.

In operation, an electronic signal is being sent through fault diaphragm22 from power source 50. Because fault diaphragm 22 is not in contactwith alarm diaphragm 24 when there are below normal pressure conditions,an electrical circuit between the two is open. The electrical signalfrom power source 50 will not travel through fault diaphragm 22 andalarm diaphragm 24 to electronic controller 52. Electronic controller 52will register that there is no electrical signal coming in and will sendout a signal along path D indicating that there are below normalpressure conditions in switch 12.

Below normal pressure conditions can occur when there is a leak,disconnect, or other problem in pressure tube 32 or switch 12. If thereis a leak or disconnect, the pressure in pressure tube 32 and cavity 30of switch 12 will decrease. As the pressure decreases, both alarmdiaphragm 24 and fault diaphragm 22 will retain their normalconfigurations and will not be touching. This will open the circuitbetween alarm diaphragm 24 and fault diaphragm 22 and will prevent asignal from traveling along path B to electronic controller 52. The lackof a signal entering electronic controller 52 will indicate that thereis a fault condition in the system. Electronic controller 52 can thensend a signal along path D indicating that there is a fault condition inswitch 12.

FIG. 2A shows a side cross-sectional view of APD 10 with piston 44 in afirst position. FIG. 2A depicts switch 12 at normal pressure conditionswith piston 44 in a first position. In the embodiment shown, normalpressure conditions exist under normal operating temperatures. Normaloperating temperatures exist between a pre-set fault temperature and apre-set alarm temperature. The pre-set fault temperature defines a lowerlimit of the normal operating temperatures and is the point at whichpressure conditions will drop below normal. Fault diaphragm 22 willdeform when the temperature rises above the pre-set fault temperature.The pre-set alarm temperature defines an upper limit of the normaloperating temperatures and is the point at which pressure conditionswill rise above normal. Alarm diaphragm 24 will deform when thetemperature rises above the pre-set alarm temperature. Normal pressureconditions thus exist between the pre-set fault temperature and thepre-set alarm temperature. At normal pressure conditions, faultdiaphragm 22 deforms and comes into contact with alarm diaphragm 24.

Under normal pressure conditions, electrical power is being sent tofault diaphragm 22 from power source 50. When fault diaphragm 22 comesinto contact with alarm diaphragm 24 under normal pressure conditions,an electrical circuit between the two is closed and the electric signalfrom power source 50 will travel through fault diaphragm 22 to alarmdiaphragm 24. This electric signal can then travel through alarmdiaphragm 24 and along path B to electronic controller 52. Electroniccontroller 52 will register this electric signal and will send out asignal along path D indicating that there are normal pressure conditionsin switch 12.

In FIG. 2A, piston 44 and magnet 48 are occupying positions alongpressure tube 32 where piston 44 and magnet 48 were positioned when APD10 was assembled. Under normal operating conditions, piston 44 andmagnet 48 can remain un-moved along pressure tube 32. Throughout thelife cycle of the aircraft, piston 44 and/or magnet 48 may oscillate dueto vibrations in APD 10 from the aircraft. As piston 44 oscillates or isjostled within pressure tube due to aircraft vibrations, passage 46allows gas pressure to pass through passage 46 thereby equalizing apressure differential between first chamber 34 and second chamber 36,which prevents switch 12 from activating. Without passage 46 in piston44, small oscillations of piston 44 could cause an abrupt pressurechange within cavity 30 and potential activation of at least one offault diaphragm 22 and alarm diaphragm 24 indicating a false fault oralarm condition. Passage 46 permits piston 44 to oscillate in smalllinear movements if one of internal stops 38 breaks. Therefore, by nothaving piston 44 be so reactive to the normal pressure fluctuationsexperienced during a typical flight cycle, the risk of false firewarnings or false failure indications is minimized.

Utilizing the combination of piston 44 and magnet 48 with pressure tube32 in APD 10 is advantageous because switch 12 can now send a signalthat indicates which state switch 12 currently occupies without the needfor completely removing APD 10 from the aircraft. This allows a user toverify that switch 12 is operable and that APD10 is functioningnormally.

FIG. 2B shows a side cross-sectional view of APD 10 with piston 44 in asecond position. Piston 44 has been moved towards housing 30 (to theleft in FIG. 2B) in response to moving magnet 48 towards housing 30. Inresponse to moving piston 44, the pressure of the gas within firstchamber 34 and cavity 30 has increased. In response the increasedpressure of the gas in first chamber 34 and cavity 30, both faultdiaphragm 22 and alarm diaphragm 24 will deform. This will cause faultdiaphragm 22 to come into contact with alarm diaphragm 24 and it willcause alarm diaphragm 24 to come into contact with contact pin 20.

In operation, electrical power is being sent through fault diaphragm 22from power source 50. When fault diaphragm 22 comes into contact withalarm diaphragm 24 in response to piston 44 moving closer to housing 14,an electrical circuit between the two is closed and the electric signalfrom power source 50 will travel through fault diaphragm 22 to alarmdiaphragm 24. When alarm diaphragm 24 comes into contact with contactpin 20, an electrical circuit between them is closed and the electricsignal will travel through alarm diaphragm 24 to contact pin 20. Thiselectric signal can then travel through contact pin 20 and along path Cto electronic controller 52. Electronic controller 52 will register thiselectric signal and will send out a signal along path D indicating thatswitch 12 occupies a first test phase, which under normal operatingconditions would indicate an alarm condition.

As piston 44 is moved closer to housing 14, the pressure in pressuretube 32 will increase, which will increase the pressure in cavity 30 ofintegrated switch 12. If the pressure gets above a pre-set alarmpressure of switch 12, the pressure will get high enough to cause alarmdiaphragm 24 to deform and come into contact with contact pin 20. Thiscloses the circuit between alarm diaphragm 24 and contact pin 20 andcauses an electric signal to travel between the two. This signal will besent to electronic controller 52. Electronic controller 52 can then senda signal indicating that switch 12 occupies the first test phase (e.g.,an alarm condition).

FIG. 2C shows a side cross-sectional view of APD 10 with piston 44 in athird position. Piston 44 has been moved away from housing 30 (to theright in FIG. 2B) in response to moving magnet 48 away from housing 30.In response to moving piston 44, the pressure of the gas within firstchamber 34 and cavity 30 has decreased. In response the decreasedpressure of the gas in first chamber 34 and cavity 30, both faultdiaphragm 22 and alarm diaphragm 24 will form back into a non-deformedstate. This will cause both fault diaphragm 22 and alarm diaphragm 24 tocome back into in their normal non-deformed configuration and they willnot be touching.

In operation, an electrical signal is being sent through fault diaphragm22 from power source 50. Because fault diaphragm 22 is not in contactwith alarm diaphragm 24 when piston 44 is moved away from housing 44, anelectrical circuit between the two is open. The electric signal frompower source 50 will not travel through fault diaphragm 22 and alarmdiaphragm 24 to electronic controller 52. Electronic controller 52 willregister that there is no electric signal coming in and will send out asignal along path D indicating that switch 12 occupies a second testphase, which under normal operating conditions would indicate an faultcondition.

When piston 44 is moved away from housing 14 and towards endcap 42, thepressure in first chamber 34 and cavity 30 of integrated switch 12 willdecrease. As the pressure decreases in first chamber 34 and cavity 30,both alarm diaphragm 24 and fault diaphragm 22 will retain their normalconfigurations and will not be touching. This will open the circuitbetween alarm diaphragm 24 and fault diaphragm 22 and will prevent asignal from traveling along path B to electronic controller 52. The lackof a signal entering electronic controller 52 will indicate that switch12 occupies the second test phase (e.g., fault condition). Electroniccontroller 52 can then send a signal along path D indicating that thereis a fault condition in integrated switch 12.

FIGS. 2A-2C provide examples of a method of testing switch 12 in APD 10.The method of testing switch 12 in APD 10 can include attaching magnet48 to pressure tube 32 of APD 10. Piston 44 is moved within pressuretube 32 with magnet 48 surrounding a portion of pressure tube 32. Apressure of a gas in a portion of pressure tube 32 is adjusted inresponse to moving piston 44. A state of switch 12 is monitored. Switch12 is set in a test phase in response to the pressure adjustment of thegas in pressure tube 32. Setting switch 12 in a test phase includesactivating at least one of fault diaphragm 22 and alarm diaphragm 24located in switch 12 in response to the pressure adjustment of the gasin pressure tube 32. An electrical signal is activated to indicate thestate of at least one of fault diaphragm 22 and alarm diaphragm 24.Switch 12 is set into a normal operational phase.

FIG. 3 shows a flowchart illustrating method 300 of assembling APD 10.Method 300 includes steps 302 through 318. Step 302 includes placingpiston 44 within pressure tube 32 of switch 12 of APD 10. Step 304includes charging switch 12 with gas. Step 304 also includes step 306 ofsupplying an inert gas into switch 12 and pressure tube 32. The inertgas can be supplied into switch 12 through at least one of

Step 308 includes calibrating APD 10. Calibrating APD 10 includesvarious additional steps. For example, computational fluid dynamics areused to model the engine of the aircraft. Functional hazard analysis offire threats are completed in regions of the engine that need heatand/or fire protection. A fire threat is determined based on a maximumallowable temperature. The maximum allowable temperature is thencross-referenced with the design capabilities of APD 10. Some additionalsteps can be performed including determining a maximum ambient safeoperating temperature, determine the full length of the alarm that isneeded to fit into the aircraft element being monitored, and determinewhich length of alarm provides adequate localized fire detection. Thesesteps are used to determine the temperature threshold of APD 10 as wellas a sufficient length of pressure tube 32. Once the temperaturethreshold and length of pressure 32 are determined, a pressure of theinert gas inside switch 12 is adjusted (step 310) such that switch 12 isactivated at temperatures matching the maximum ambient safe operatingtemperature of the location in the aircraft of pressure tube 32.Calibrating APD 10 can also include setting fault diaphragm 22 and alarmdiaphragm 24 at a predetermined distance from each other (or fromcontact pin 20) that corresponds to a distance of travel of faultdiaphragm 22 and/or alarm diaphragm 24 when pressure tube 32 reaches apredetermined pressure.

Step 312 includes hermetically sealing switch 12 by attaching endcap 42onto the end of pressure tube 32. Step 314 includes attaching magnet 48to a portion of pressure tube 32 such that magnet 48 is slidably engagedwith pressure tube 32. Step 316 includes placing magnet 48 at an axiallocation of pressure tube 32 such that a portion of magnet 48 is axiallyaligned with a portion of piston 44. Step 318 includes installing APD 10onto an aircraft.

Assembling APD 10 with method 300 allows APD 10 to function as discussedabove and provides the benefits discussed above of being able to testthe state switch 12 of APD 10 without needing to completely remove APD10 from the aircraft.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

An advance pneumatic detector to indicate pressure changes in anenvironment includes a switch, a pressure tube, an endcap, a piston, anda magnet. The pressure tube is connected to the switch. The endcap isdisposed on an end of the pressure tube opposite from the switch. Thepiston is disposed within and forms a seal against the pressure tube.The piston is slidably engaged with the pressure tube. The magnet isslidably attached to and surrounds a portion of the pressure tube. Themagnet is configured to control the positioning of the piston within thepressure tube.

The advance pneumatic detector of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components.

The switch can further comprise a housing with a cavity between a firstretainer portion and/or a second retainer portion, wherein the cavity isin fluid communication with the pressure tube and the piston, a contactpin can be held in the first retainer portion, a fault diaphragm can beheld in the cavity of the housing near the second retainer portion,and/or an alarm diaphragm can be held in the cavity of the housing nearthe first retainer portion.

At least one of the piston and the magnet can comprise a permanentmagnet and/or an electromagnet.

The piston can comprise a passage that can extend through the piston.

The piston can divide the pressure tube into a first chamber and/or asecond chamber, the first chamber can be between the housing and thepiston and the second chamber can be between the piston and the endcap,and the passage can fluidly connect the first chamber and the secondchamber.

A method for testing a switch in an advance pneumatic detector with apressure tube can include moving a piston within the pressure tube witha magnet. A pressure of a gas in a portion of the pressure tube can beadjusted in response to moving the piston. A state of the switch can bemonitored.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components.

Monitoring the state of the switch can comprise setting the switch in atest phase in response to the pressure adjustment of the gas in thepressure tube

Setting the switch in a test phase can comprise activating a diaphragmlocated in the switch in response to the pressure adjustment of the gasin the pressure tube.

An electrical signal to indicate the state of the diaphragm can beactivated.

The switch can be set into a normal operational phase.

The magnet can be attached to the pressure tube of the advance pneumaticdetector.

A method of assembling an advance pneumatic detector can include placinga piston within a pressure tube of a switch of the advance pneumaticdetector. The switch can be charged with gas. The switch can behermetically sealed. The advance pneumatic detector can be calibrated. Amagnet can be positioned to surround a portion of the pressure tube suchthat the magnet can be slidably engaged with the pressure tube.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components.

The advance pneumatic detector can be installed onto an aircraft.

Calibrating the advance pneumatic detector can comprise adjusting apressure of an inert gas inside the switch.

Charging the switch can comprise inserting an inert gas into the switchand/or the pressure tube.

Attaching the magnet can comprise placing the magnet at an axiallocation of the pressure tube such that a portion of the magnet can beaxially aligned with a portion of the piston.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A method for testing a switch in an advance pneumatic detector with apressure tube, the method comprising: moving a piston within thepressure tube with a magnet; adjusting a pressure of a gas in a portionof the pressure tube in response to moving the piston; and monitoring astate of the switch.
 2. The method of claim 1, wherein monitoring thestate of the switch comprises setting the switch in a test phase inresponse to the pressure adjustment of the gas in the pressure tube. 3.The method of claim 2, wherein setting the switch in a test phasecomprises activating a diaphragm located in the switch in response tothe pressure adjustment of the gas in the pressure tube.
 4. The methodof claim 3 further comprising activating an electrical signal toindicate the state of the diaphragm.
 5. The method of claim 1 furthercomprising setting the switch into a normal operational phase.
 6. Themethod of claim 1 further comprising attaching the magnet to thepressure tube of the advance pneumatic detector.
 7. A method ofassembling an advance pneumatic detector, the method comprising: placinga piston within a pressure tube of a switch of the advance pneumaticdetector; charging the switch with gas; hermetically sealing the switch;calibrating the advance pneumatic detector; and attaching a magnet to aportion of the pressure tube, wherein the magnet is slidably engagedwith the pressure tube.
 8. The method of claim 7 further comprisinginstalling the advance pneumatic detector onto an aircraft.
 9. Themethod of claim 7, wherein calibrating the advance pneumatic detectorcomprises adjusting a pressure of an inert gas inside the switch. 10.The method of claim 7, wherein charging the switch comprises insertingan inert gas into the switch and the pressure tube.
 11. The method ofclaim 7, wherein attaching the magnet comprises placing the magnet at anaxial location of the pressure tube such that a portion of the magnet isaxially aligned with a portion of the piston.